Water-based fluids have been used commercially for many years as a means of transmitting energy in hydraulic systems. Among such water-based fluids are the water-soluble glycol or glycol ether-containing compositions (hereinafter "water-glycol" type fluids) disclosed, for example, in U.S. Pat. Nos. 2,558,030 and 2,602,780 both to Zisman et al., and U.S. Pat. No. 2,768,141 to Langer et al.
Compared to petroleum-based fluids, water-glycol type fluids generally have low flammibility, and good temperature stability. Moreover, clean-up and disposal are usually more convenient when utilizing water-glycol type fluids as opposed to petroleum-based compositions. However, water-glycol type energy transmitting fluids, such as are disclosed by the above-cited patents, generally have relatively poor lubricating and anti-wear properties in high pressure applications.
Various lubricity and/or anti-wear additives have been suggested in attempts to improve the performance of water-glycol type energy transmitting fluids.
U.S. Pat. No. 2,947,699 to Wasson, et al. discloses the use of alkali metal soaps of an organic aliphatic acid as an anti-wear agent in water-glycol type hydraulic fluids.
U.S. Pat. No. 4,493,777 to Snyder, Jr., et al. discloses a water-based hydraulic fluid having incorporated therein as an antiwear or lubricity agent, the metal or amine salt of an organo sulfur, phosphorous, boron or carboxylic acid.
U.S. Pat. No. 3,992,312 to Genjida, et al. discloses a water-glycol base hydraulic fluid comprising from about 30-60 weight percent of water; from about 5-30 weight percent of a water-soluble polymer containing (1) a residue of a polyamide having active hydrogen atoms and (2) oxyalkylene groups bonded to the residue; and from about 15-60 weight percent of a glycol, said fluid being disclosed as having good lubricating and wear preventing qualities.
U.S. Pat. No. 4,434,066 to Lewis discloses a water-glycol type fluid composition having incorporated therein between about 0.1 to 10 percent by weight of an acidic lubricity agent (i.e., saturated and unsaturated carboxylic and polycarboxylic acids having at least 6 carbon atoms, aromatic carboxylic acids, alkali metal or organic amine salts of said carboxylic acids, polymerized fatty acids, oxycarboxylic acids and dicarboxylic acids), and between about 0.01 and about 10 percent by weight of an anti-wear agent (i.e., a combination of an hydroxyl-substituted aromatic acid component and a nitroaromatic compound component).
U.S. Pat. No. 4,390,439 to Schwartz et al. discloses the use of neodecanoic acid to improve to anti-wear and corrosion-inhibiting properties of hydraulic fluids having a water content of from about 60 to about 99 weight percent.
The disclosures of the prior art regarding the enhanced lubricity and anti-wear benefits of additive containing fluids notwithstanding, prior to this invention the lubricity and wear characteristics of water-glycol type fluids have limited the use of such fluids to systems operating at pressures of less than about 3,000 psi.
Accordingly, it is an object of this invention to provide a water-glycol type energy transmitting fluid having enhanced high pressure performance.